1. Field of the Invention
This invention is directed to a process for solvent cleaning the internal surfaces of polyvinyl halide reactors and for recovering the solvent used therein for reuse in the cleaning step.
Manual cleaning of the polymerization reaction equipment can be eliminated by practicing this invention. This has particular importance in light of the harmful nature of the vinyl halides such as vinyl chloride used in the polymerization reaction and the recent governmental regulations concerning the exposure of personnel to vinyl chloride.
2. Description of the Prior Art
There are at least two known methods for chemically removing vinyl halide polymeric residues adhering to the internal surfaces of the polymerization equipment and for recovering the solvent for reuse.
One such process is disclosed in Torrenzano et al, U.S. Pat. Re, 27,432. The essential features of the Torrenzano process comprises contacting the residual build up of polymeric materials from vinyl halide polymerization vessels with a solvent such as tetrahydrofuran (THF) which has an atmospheric boiling point of 66.degree. C, and then contacting the solution with the polymers dissolved therein with steam to flash distill the THF for its recovery and reuse. The residual materials such as water, some THF and precipitated polymers are discarded as waste. This process requires the use of solvents that have boiling points below that of water or that form an azeotrope that has a boiling point below that of water.
Another prior art solvent cleaning and recovery process is disclosed in Berni, U.S. Pat. No. 3,764,384. The Berni process comprises contacting the build up of polyvinyl halide on the surfaces of the polymerization equipment with N-methyl pyrrolidone, adding 20 to 50% by volume of water to the residue-solvent solution to precipitate the polymeric residues and separating the precipitate from the aqueous N-methyl pyrrolidone solution by either filtration or centrifugation. The latter is dehydrated for reuse and the polymeric precipitate is incinerated or otherwise discarded. The disadvantages of this process are that it loses too much water and solvent and a precipitate is formed in the process that is not easily separated from the solvent.